In drilling an oil well, a natural gas well, and a geothermal well, materials are used to cement an annular cavity between a stratum and a casing pipe, which are so-called a cement slurry composition for well. In general, a cement slurry is fed into an annular cavity between a casing pipe and a stratum with a pump via the casing pipe from the ground. The annular cavity is filled with the cement slurry upward from the bottom thereof. The casing piper is fixed in the well with the hardened cement slurry, and thereby the inner wall of the well is protected.
Conventional cement slurry compositions for well used to cement a well have contained various additives. Examples of the additive include a cement accelerator, a cement retarder, a dispersant, a cement dehydration-reducing agent, a low-density additive, a high-density additive, an expanding agent, a cement strength stabilizer and a silica powder. These are used in combination according to well conditions and a purpose.
In cementing a well, a defect easily occurs in a cemented part by material segregation and running into cracks in the well. To address this, walnut shells, cotton seeds, clay minerals, and polymer compounds and the like have conventionally been added. JP-A10-36825 discloses a cement slurry for geothermal well containing a pulverized portland cement and a specific finely powdered silicaceous admixture. JP-A06-42281 discloses a method of preventing water leakage with a specific cement slurry to which a retarder such as a boron compound and a lignosulphonic acid derivative is added. JP-A09-13034 discloses a specific cement slurry composition for well containing a cement, β-1,3-glucan, a dispersant, and an antifoaming agent. JP-A2003-313537 discloses a slurry without diluting in water, containing a slurry rheology modifier prepared with specific compounds (A) and (B).
Further, JP-A 2004-124007 discloses a slurry rheology modifier of a single agent type. U.S. Pat. No. 7,374,699 discloses a slurry rheology modifier which is a combination of two kinds of water-soluble low molecular weight compound.